Influence of Anionic Surfactants on the Fundamental Properties of Polymer/Reduced Graphene Oxide Nanocomposite Films.

Surfactants are frequently employed in the fabrication of polymer/graphene-based nanocomposites via emulsion techniques. However, the impact of surfactants on the electrical and mechanical properties of such nanocomposite films remains to be explored. We have systematically studied the impact of two anionic surfactants [sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS)] on intrinsic properties of the nanocomposite films comprising reduced graphene oxide in a matrix of poly(styrene-stat-n-butyl acrylate). Using these ambient temperature film-forming systems, we fabricated films with different concentrations of the surfactants (1-7 wt %, relative to the organic phase). Significant differences in film properties were observed both as a function of amount and type of surfactant. Thermally reduced films exhibited concentration-dependent increases in surface roughness, electrical conductivity, and mechanical properties with increasing SDS content. When compared with SDBS, SDS films exhibited an order of magnitude higher electrical conductivity values at every concentration (highest value of ∼4.4 S m-1 for 7 wt % SDS) and superior mechanical properties at higher surfactant concentrations. The present results illustrate how the simple inclusion of a benzene ring in the SDS structure (as in SDBS) can cause a significant change in the electrical and mechanical properties of the nanocomposite. Overall, the present results demonstrate how nanocomposite properties can be judiciously manipulated by altering the concentration and/or type of surfactant.

Synthesis of diamine functionalised graphene oxide and its application in the fabrication of electrically conducting reduced graphene oxide/polymer nanocomposite films.

The focus of research in diamine functionalised graphene oxide (GO) has been limited to the use of diamines either as crosslinker or to achieve simultaneous functionalisation, reduction and stitching of GO sheets, especially in the case of ethylene diamine (EDA). Controlling the extent of stitching and functionalisation has to date remained a challenge. In particular, synthesis of colloidally stable monofunctionalised GO-NH2 with dangling amine groups using diamines has remained elusive. This has been the limiting factor towards the utility of EDA functionalised GO (GO-NH2) in the field of polymer-based nanocomposites. We have synthesised colloidally stable GO-NH2 with dangling amine groups and subsequently demonstrated its utility as a surfactant to synthesize colloidally stable waterborne polymer nanoparticles with innate affinity to undergo film formation at room temperature. Thermally annealed dropcast polymer/GO-NH2 nanocomposite films exhibited low surface roughness (∼1 µm) due to the homogeneous distribution of functionalised GO sheets within the polymer matrix as observed from confocal laser scanning microscopy, scanning electron microscopy and transmission electron microscopy. The films exhibited considerable electrical conductivity (∼0.8 S m-1), demonstrating the potential of the GO-NH2/polymer nanocomposite for a wide range of applications.